Extirpated Wildlife said:
Yes, there is. Your saying in macro evolution that a walrus could evolve into a dog.
One of the most puzzling things for someone trying to understand macro-evolution is why scientists affirm that mammals did evolve from reptiles and at the same time say a walrus will never evolve into a dog. After all a walrus is already more like a dog than a reptile is, so why not?
The answer to this puzzle is the study of phylogeny--which is basically the study of the
history of evolution as distinct from figuring out how evolution happens.
Evolution does mean change in species. But which changes can occur are constrained by the changes of the past. It is not possible for any species to become any other species or even any other sort of species. The options for change in any species are limited by the past history of the species lineage.
The evidence does show that one group of ancient reptiles (therapsids) did evolve into mammals. Not all of them. But changes kept occuring within that lineage such that at some point they had more mammalian than reptilian characteristics.
This does not mean that any other reptiles did, can or ever will become mammals. Nor does it mean that any mammals can ever become reptiles.
Walruses will never become dogs or vice versa. However, both are derived from a carnivorous mammalian ancester that was neither a walrus nor a dog. Some of the far distant descendants of walruses may be different enough from today's species that scientists of the future will give them a different name. But they will still be recognized as descendants of walruses. Ditto for dogs.
The image of the branching bush (aka the nested hierarchy) is crucial to understanding the pathways evolution has taken in the past and the constraints which limit evolution in the present and future.
Species change is not a free-for-all whereby anything has unlimited capacity to become something else. There are rules that limit the options. But within those rules the extent of bio-diversity past and present are still truly amazing.
Most of this does not require faith, but simply a good acquaintance with phylogeny and the evidence in which it is grounded. Two sites I recommend are
http://www.ucmp.berkeley.edu/historyoflife/histoflife.html
and
http://tolweb.org/tree/phylogeny.html
Here is a commentary specifically on human evolution.
http://home.comcast.net/~aronra/Taxonomy.html